Water heaters are commonly used in homes, businesses and just about any establishment having the need for heated water. In many cases, a water heater is configured to heat water in a water heater tank using a gas-fired burner, an electric heater or some other heater element. When demand for hot water arises (e.g., someone turns on a faucet to run a shower), fresh, cold or ambient temperature water typically enters the water heater tank and “pushes out” or supplies the hotter water. When the temperature of the water in the water heater falls below a temperature set point, either though the mere passage of time or as a result of a hot water draw, the water heater typically activates a heater element to restore the temperature of the water in the tank back to the temperature set point.
To help reduce cycling of the water heater, a temperature differential is often employed, where the water heater does not activate the heater element until the temperature of the water in the water heater falls below the temperature set point by at least a temperature differential amount. The desired temperature set point can be referred to as the first temperature set point and the temperature at which the heater element is actually activated can be referred to as the second temperature set point, where the difference between the first temperature set point and the second temperature set point corresponds to the temperature differential.
A conventional water heater typically has at least one heating element or “heater,” such as a gas-fired and/or electric burner. To take advantage of the “heat-rises” principle, the heater is often located at or near the bottom of the water heater tank. Each water heater typically also has at least one thermostat or controller for controlling the heater. To facilitate the heating of water, the controller often receives signals related to the temperature of the water, oftentimes from a temperature sensor that is thermally engaged with the water within the water heater. When temperature signals from the temperature sensor indicate that the water temperature is below the second temperature set point, for example when the water temperature is below about 120° F., the controller may turn on the heater element and the water within the water heater begins to heat. After some time, the water temperature within the water heater tank may increase back to the first temperature set point, which, for example, may be about 140° F. At this point, the controller may cause the heater element to reduce its heat output or, alternatively, causes the heater element to turn off. This heating cycle may begin again when the water temperature within the water heater tank drops below the second temperature set point.
Water heaters are typically available in a variety of different sizes so that a particular home or building may be equipped with a water heater having a thermal capacity, or quantity of sufficiently heated water, that is sufficient for normal conditions expected for the particular home or building. However, special circumstances, such as having overnight visitors, may mean that there may be a temporary, larger than normal demand for hot water. Typically, the increased demand is accompanied by a need to have increased hot water available within a relatively short time frame. For example, several extra house guests may wish to shower in the morning, causing a temporary increased demand for hot water in a relatively short time period. One way to accommodate this situation is to initially install an oversized water heater. However, it may not be very efficient to run an oversized water heater all the time to accommodate occasional and short-term demands for increased hot water.